The disclosure of Japanese Patent Application No. 2003-017043 filed on Jan. 27, 2003 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a combustion control apparatus and a combustion control method for an in-cylinder injection internal combustion engine.
2. Description of the Related Art
In an internal combustion engine mounted in an automobile or the like, the temperature of a catalyst is increased by increasing the temperature of exhaust gas in a warming-up process after the engine is started such that the catalyst is activated and necessary exhaust gas purification performance can be obtained early after the engine is started. Japanese Patent Laid-Open Publication No. 10-169488 proposes an in-cylinder injection internal combustion engine in which compression stroke injection is executed in an engine warming-up process from when the engine is started until when an increase in the temperature of a catalyst is completed such that the temperature of exhaust gas is increased, thereby increasing the temperature of the catalyst.
In the case where heavy fuel that has lower volatility than standard fuel is used in the in-cylinder injection internal combustion engine, combustion may deteriorate while the compression stroke injection is executed in the engine warming-up process. When the compression stroke injection is executed, ignition is performed while there is a combustible fuel-air mixture around an ignition plug, whereby combustion is performed. However, in the case where the compression stroke injection is executed in the engine warming-up process, and the heavy fuel having low volatility is used, it is difficult to allow a fuel-air mixture with a fuel concentration necessary for stable combustion to remain around the ignition plug at the time of ignition. Therefore, while the compression stroke injection is executed in the engine warming-up process in the case where the heavy fuel is used, combustion may deteriorate and the engine speed may drop, which may cause a stall or rough idling.
In order to address such problems due to use of the heavy fuel, it is proposed to perform a stabilization control which stabilizes combustion when the engine speed drops in the engine warming-up process. Examples of the stabilization control include a control that increases a fuel injection amount, which is disclosed in Japanese Patent Laid-Open Publication No. 8-4571, and a control that advances ignition timing, which is disclosed in Japanese Patent Laid-Open Publication No. 9-158774.
In the case where the aforementioned control that increases the fuel injection amount is executed, the fuel concentration of the air-fuel mixture around the ignition plug at the time of ignition is increased, whereby deterioration of the combustion due to use of heavy fuel can be suppressed when injection is executed in the engine warming-up process and heavy fuel is used. Also, when the temperature of the catalyst is increased in the engine warming-up process, preference is given to the increase in the temperature of the exhaust gas over realization of stable combustion, and the ignition timing is generally delayed. Since the delay amount of the ignition timing is decreased by the aforementioned control that advances the ignition timing, deterioration of the combustion is suppressed in the case where the compression stroke injection is executed in the engine warming-up process and heavy fuel is used.
Meanwhile, the engine speed may temporarily drop in the case where disturbance such as resistance when a vehicle takes off is applied to the internal combustion engine. The fuel injection amount is increased or the ignition timing is delayed by the stabilization control also based on such a temporary drop of the engine speed due to reason other than unstable combustion. In this case, a controlled variable such as the fuel injection amount or the ignition timing deviates from the optimum value for performing desired operation of the engine, which leads to deterioration of fuel efficiency and exhaust gas emission.
Accordingly, it is preferable that the stabilization control based on the drop of the engine speed should be executed, for example, only during a period from when the engine is started until when the combustion by the compression stroke injection is stabilized in the engine warming-up process, and the stabilization control should be stopped after the combustion is stabilized in the middle of execution of the compression stroke injection. By limiting the execution period of the stabilization control in this manner, an unnecessary increase in the fuel injection amount or unnecessary advance of the ignition timing based on the temporary drop of the engine speed due to disturbance can be suppressed, and therefore, deterioration of fuel efficiency and exhaust gas emission can be suppressed as much as possible.
In the in-cylinder injection internal combustion engine, in the case where the compression stroke injection is executed for increasing the temperature of the catalyst in the engine warming-up process, a fuel injection mode is switched from the compression stroke injection to intake stroke injection when the increase in the temperature of the catalyst is completed. In the case of the intake stroke injection, fuel injected into a combustion chamber is easily diffused in the combustion chamber until ignition. Therefore, the fuel concentration of the air-fuel mixture around the ignition plug at the time of ignition tends to be low in the engine warming-up process. Accordingly, the time required for the fuel concentration to reach a level necessary for obtaining stable combustion is long, as compared with the compression stroke injection.
Thus, in the case where heavy fuel having low volatility is used, when the fuel injection mode is switched from the compression stroke injection to the intake stroke injection after the increase in the temperature of the catalyst is completed as described above, it becomes difficult to allow the air-fuel mixture with a fuel concentration necessary for obtaining stable combustion to remain around the ignition plug at the time of ignition by the intake stroke injection. Thus, the combustion becomes unstable after the intake stroke combustion is started, which causes the engine speed to drop.
However, even if the engine speed drops due to unstable combustion after the intake stroke injection is started, the fuel injection amount cannot be increased and the ignition timing cannot be advanced based on the drop of the engine speed, since the stabilization control for suppressing the unstable combustion is stopped when the combustion is stabilized in the middle of execution of the compression stroke injection. Accordingly, the drop of the engine speed cannot be suppressed, and rough idling is caused due to the drop of the engine speed.
It is an object of the invention to provide a combustion control apparatus and a combustion control method for an in-cylinder injection internal combustion engine, which do not unnecessarily execute a stabilization control while compression stroke injection is executed after the engine is started, and can appropriately suppress unstable combustion by the stabilization control when a fuel injection mode is switched from the compression stroke injection to intake stroke injection.
A first aspect of the invention relates to a combustion control apparatus for an in-cylinder injection internal combustion engine including a stabilization controller, an execution stop controller, and a restart controller. The stabilization controller executes a stabilization control that stabilizes combustion by changing a controlled variable used for controlling operation of the engine when an engine speed drops in an engine warming-up process after the engine is started, wherein compression stroke injection is executed in the engine warming-up process. The execution stop controller limits an execution period of the stabilization control during which the stabilization control is executed, and stops the stabilization control in the middle of execution of the compression stroke injection. The restart controller restarts the stabilization control when a fuel injection mode is switched from the compression stroke injection to intake stroke injection.
With the aforementioned configuration, the stabilization control which is executed while the compression stroke injection is executed in the engine warming-up process can be stopped when the combustion by the compression stroke injection becomes stable, whereby an unnecessary change in the controlled variable for the internal combustion engine can be suppressed while the compression stroke injection is executed. Also, since the stabilization control is restarted when the fuel injection mode is switched from the compression stroke injection to the intake stroke injection, the controlled variable for the internal combustion engine is changed by the stabilization control for stabilizing the combustion when the combustion becomes unstable due to volatility of fuel used for the internal combustion engine and the like, and the engine speed drops while the intake stroke injection is executed. Thus, it is possible to suppress the drop of the engine speed, and occurrence of a stall or rough idling due to the drop of the engine speed.
In the first aspect of the invention, the controlled variable may include a fuel injection amount, and the stabilization controller may stabilize the combustion by increasing the fuel injection amount. In the case where fuel having low volatility is used, a fuel concentration of a fuel-air mixture around an ignition plug at the time of ignition is low while the compression stroke injection is executed in the engine warming-up process after the engine is started, the combustion deteriorates, and the engine speed drops. With the aforementioned configuration, the fuel injection amount is increased by the stabilization control based on the drop of the engine speed, and the fuel concentration of the fuel-air mixture around the ignition plug at the time of ignition is suppressed from becoming low. Thus, it is possible to suppress the deterioration of the combustion due to use of fuel having low volatility, and to suppress the drop of the engine speed and occurrence of a stall or rough idling due to the drop of the engine.
In the aforementioned aspect of the invention, the stabilization controller may decide an increase amount of the fuel injection amount based on a drop amount of the engine speed. Thus, since a volatility amount of the fuel in a combustion chamber is increased, and the fuel concentration of the fuel-air mixture around the ignition plug at the time of ignition becomes higher due to the increase in the fuel injection amount, the deterioration of the combustion due to use of heavy fuel can be suppressed in the case where the compression stroke injection is executed in the engine warming-up process and the heavy fuel is used.
In the aforementioned aspect of the invention, the stabilization controller may gradually decrease the increase amount of the fuel injection amount with time. When the engine temperature is gradually increased after the fuel injection amount is increased, the volatility of the fuel in the combustion chamber becomes higher, and the fuel concentration of the fuel-air mixture around the ignition plug at the time of ignition becomes higher. Thus, since the increase amount of the fuel injection amount is gradually decreased as the fuel concentration becomes higher, the fuel concentration can be suppressed from becoming extremely high.
In the aforementioned aspect of the invention, the controlled variable may include at least one of a fuel injection amount and ignition timing, and the stabilization controller may stabilize the combustion by at least one of increasing the fuel injection amount and advancing the ignition timing.
In the aforementioned aspect of the invention, the stabilization controller may decide an advance amount of the ignition timing based on a drop amount of the engine speed.
In the aforementioned aspect of the invention, ignition timing of the internal combustion engine may be controlled to be delayed by a predetermined delay amount while the compression stroke injection is executed in the engine warming-up process, the controlled variable may include the ignition timing, and the stabilization controller may stabilize the combustion by advancing the ignition timing by making a delay amount become smaller than the predetermined delay amount. While the compression stroke injection is executed in the engine warming-up process, preference is given to warming-up of an exhaust emission control catalyst and the like over the stabilization of the combustion, and therefore the ignition timing is controlled to be delayed by the predetermined delay amount so as to increase the temperature of exhaust gas. With the aforementioned configuration, the ignition timing is advanced by decreasing the delay amount by the stabilization control based on the drop of the engine speed. Thus, the combustion is stabilized, the drop of the engine speed can be suppressed, and occurrence of a stall or rough idling due to the drop of the engine speed can be suppressed.
In the aforementioned aspect of the invention, the controlled variable may include both a fuel injection amount and ignition timing, and the stabilization controller may stabilize the combustion by both increasing the fuel injection amount and advancing the ignition timing when a drop amount of the engine speed is larger than a predetermined amount; and the controlled variable may include only the fuel injection amount, and the stabilization controller may stabilize the combustion only by increasing the fuel injection amount among increasing the fuel injection amount and advancing the ignition timing when the drop amount of the engine speed is smaller than the predetermined amount. When the drop of the engine speed is small, the drop of the engine speed can be suppressed by increasing the fuel injection amount. Thus, since the ignition timing is not advanced when the drop amount of the engine speed is smaller than the predetermined amount, it is possible to suppress inhibition of the increase in the temperature of the exhaust gas and the like due to unnecessary advance of the ignition timing.
In the aforementioned aspect of the invention, the stabilization controller may change the execution period of the stabilization control after the engine is started based on an engine temperature when the engine is started. Since the volatility of the fuel in the combustion chamber varies depending on the engine temperature, the period during which the drop of the engine speed due to the low fuel concentration of the fuel-air mixture around the ignition plug at the time of ignition needs to be controlled by the stabilization control, that is, the period during which the combustion becomes unstable varies depending on the engine temperature. Thus, since the execution period of the stabilization control can be changed, the execution period can be set to a required minimum period, and the drop of the engine speed can be appropriately suppressed.
In the aforementioned aspect of the invention, the stabilization controller may change the execution period of the stabilization control that is restarted based on an engine temperature when the fuel injection mode is switched. Since the volatility of the fuel in the combustion chamber varies depending on the engine temperature, the period during which the drop of the engine speed due to the low fuel concentration of the fuel-air mixture around the ignition plug at the time of ignition needs to be controlled by the stabilization control, that is, the period during which the combustion becomes unstable varies depending on the engine temperature. Thus, since the execution period of the stabilization control can be changed, the execution period can be set to a required minimum period, and the drop of the engine speed can be appropriately suppressed.
A second aspect of the invention relates to a combustion control apparatus for an in-cylinder injection internal combustion engine including stabilization means, execution stop means, and restart means. The stabilization means executes a stabilization control that stabilizes combustion by changing a controlled variable used for controlling operation of the engine when an engine speed drops in an engine warming-up process after the engine is started, wherein compression stroke injection is executed in the engine warming-up process. The execution stop means limits an execution period of the stabilization control during which the stabilization control is executed, and stops the stabilization control in the middle of execution of the compression stroke injection. The restart means restarts the stabilization control when a fuel injection mode is switched from the compression stroke injection to intake stroke injection.
A third aspect of the invention relates to a combustion method for an in-cylinder injection internal combustion engine includes a first step of executing a stabilization control that stabilizes combustion by changing a controlled variable used for controlling operation of the engine when an engine speed drops in an engine warming-up process after the engine is started, wherein compression stroke injection is executed in the engine warming-up process; a second step of limiting an execution period of the stabilization control during which the stabilization control is executed, and stopping the stabilization control in the middle of execution of the compression stroke injection; and a third step of restarting the stabilization control when a fuel injection mode is switched from the compression stroke injection to intake stroke injection.
In the third aspect of the invention, the combustion control method further includes a fourth step of stopping the stabilization control when an elapsed time since the stabilization control is restarted in the third step becomes equal to or longer than a predetermined time.